Temperature indicator



Filed Feb. i

Pay

-July 3, 1945. R. P. scHRl-:lBER Erm.

TEMPERATURE INDICATOR frequently no e Furthermore,

culty in determining Patented July 3,1945

TEMPERATURE INDICATOR Raymond Paul Schreiber and William W n, D. 0., assignors to the Goverment State! of ashingt of the United McC. Lee.

America, as represen by the Secretary of War and his successors'in cnice Application February 2, 1944, Segal No. 520,822

s mams. (ci. 'ls-ssa) (Granted under The invention described herein.. may be manufactured and used by Government for governmental purposes. wit out the payment to me oi any royalty thereon.

This invention relates to a means for indicat? ing whether or not stored food has been subjected to excessively high temperatures.

When packaged food has temperatures too high for it during transportation or storage, particular under war conditions where delay and adverse conditions are unavoidably encountered, there is xternal indication of the fact.

the deterioration of the food under excessive heat is often not 'detected after the packages are opened.v so that the food is diswith disastrous results.

some simple and inexpensive yet reliable means is needed iorindicating when food has been held under conditions which have made it unfit for use. Various prior art devices were investigated by the War Department and found unsuitable either because of buikiness and expense or inaccuracy of operation or diillwhether ornot change in their appearance had taken place.

It is an object of the present invention to provide an indicator which will show positively after an interval oi time whether orvnot it has been exposed during that time to a certain predebeen subjected to to be ilt for use, as4

termined temperature higher than is consistent with safe keeping of an object with which the indicator is associated.

It is a further object of this invention to provide a series of indicators afiected by different successively higher temperatures, so that a more accurate determinationof the highest tempermay be provided.

Specifically, it is the object of the invention indicator employing oil soluble dyes at different specified ature reached solve the dye adjacent thereto. forming an unmistakable indication that the temperature p'eculiar to the solvent showing the reaction has been reached.

A further object of the invention is to provide an -indication which is easily interpreted, since the change is from white to a denite color, and

which cannot possibly be eiiaced once it has operated, since the reaction which causes the stain is irreversible.

Further objects of the invention will be apparent from a consideration of this speciflcaf .invention in which the indication oil fast yellow,

the act of Marelr. 1883, as ainended April 30, 1928; 370 0.

linclosed in an envelo Fig. 2 is a sectional Fig. 1.

Fig. 3 is a perspective ned form o! indicator according to the invention.

view on the line 2-2 oi Fig. 4 is a sectional view on the line 4-4 of Fig. 3. f

Fig. 5 is a further modification of 'the invention in which a plurality oi indicators operable at different temperatures are provided.

Fig. 6 is a plan view oi a slightly different embodiment also having plural indicators.

Fig. I is a plan view of a modification of the as developed by exposure to heat is in the form of printed matter.

In Fig. 1 a simple embodiment of the invention is illustrated, comprising two sheets I0 and Ii ci unglazed paper. such as filter paper, inclosed in a moisture-prooi envelope I2 which is formed of two sheets il and Il of transparent material secured together around their edges. Either the two sheets IB and II or the sheets I3 and Il forming the envelope!! may, of course, be formed o1' a single sheet folded as shown in connection with Figs. 3 and 4.

0n sheet III there is imprinted a spot, layer or design I! oi' an oil soluble dye. Dyes suitable for the are oil violet, oil fast heliotrope, oil fast blue, Sudan blue KA, alizarine cyanine green base, oil fast green, Calcophenyl yellow R, Cambelline oil orange, oil orange, cerate red, or oil red. 0n sheet li there is imprinted a layer It or matching spots or designs of an oil solvent for the dye. Suitable solvents made up appropriate which they are to be to the food package with associated. In each case a solvent is chosen from the group suggested, or similar solvents, which has a melting point slightly below the point at which the particular view of a slightly moditemperatures below the melting point of of 'thermoplastic materiel, as indicated at u in Fig.A

In Fig. 7 an indicator Il of somewhat larger size but similar to that shown in Fig. 1 is provided a clean white surface as long as it is kept at time the food is to be used the by reason of the solvent having melted and ydissolved the dye, forming a stain on the paper, that the dangertemperature has been reached, the food must not be used.

vent. If at the indicator shows,

In the form of the invention in Figs. 3 and 4 the dye II and solvent I6 are printed on adiacent areas near one end of a sheet Il of an unglazed paper, and the end of the sheet is lthen folded down at I8 upon the body of` bringing the dye and solvent imprints into con- Qtact, but concealed from the observer. Theportion I9 oi the sheet which extends below the folded section is calibrated as at successively closer together. inclosed in a transparent envelope 2l a folded sheet secured together around formed of the three open edges by an adhesive or by means of heat and pressure, with or without crimping. In this modification, as in the first form described, a solvent is selected which has a melting point slightly below the maximum temperature to' which the food can be subjected without deterioration. If

during storage or transportationa higher temperature is encountered-the solvent will melt and which is in contact 'therewill dissolve the dye, with, and spreadA it through the unglazed paper, forming a visible stain. The length of the exposure to the excessive temperature can be roughly determined by noting how farthe stain has spread through the calibrated area ofthe sheet, as obviously the longer the period during which the solvent remains in a melted condition the farther the stain will spread.

In Fig. 5 a multiple indicator 24 is illustrated, which is formed in the same fashion as the indicator of Fig. 3, except thata plurality of dye and solvent areas i5 and I6 are provided within the fold at the top of the sheet 2l and a calibrated area 26 extends from each dye and solvent imprint through the body of the sheet. The areas l 26 on the sheet 25 can be separated toprevent .mingling of the dyes and solvents or travel of the the sheet. j

with lines' The sheet is then the sol'- with a printed warning 28, as "Do not eat this food or "Examine food carefully for possible spoilage." This design is formed either by printing the solvent or the dye or both in the required pattern, or by printing the unglazed paper with glazing material in the required design., In bothl cases the printed material may represent either the words themselves or the background for the words, in two cases the words remaining undyed while the background is dyed and inthe other dye stain beyond the desired area by printing or 25 with glazing prevent spreadimpregnating the unglazed sheet material in strips 21, 28 and 29 to ing of the stain. Any substancewhich willprevent penetration of the paper by the solvent, including lacquers and resins, as well as loil of higher melting points may be'employed. The indicatingarea 2B' of the indicator 24' is "shown as stained 'by the dissolved dye, sheet has been exposed totemperatureas. high as the melting point of. the solvent for that particular area, butnot as high oi' the solvent vfor theA next calibration of the areas 2B' to the melting temperature Inv the4 modification shown the time of exposure can be estimated. in Fig. 6 aplurality print I6 and havinga calibrated area adjacent thereto.v The portions of the sheet, peculiar tol each.' indicator area are separated from one anshowing that the as the melting point area 2'I'.v By proper e vof dye patches', v2| and 32 are providedeach.- comprising-a dye-'imprint I5v and aasolvent. iin-1 other .by slots lliuand '35'so vthattravel ofthe stain vfrom onearea-to adjacent areas i'sUprevented. Both forms, asl

areenclosed in transparent envelopes preferably shown in Figs. 5 and 6,

:of absorbent material two the words appearing stained on a white background.

In each of these forms the'dyes selected should have the following characteristics; it should be suitable after solution in solvent used for dyeing paper, and should be relatively insensitive to light and moisture. The dye solvent should have the following properties; itshould melt sharply at the desired temperature, it .should be relatively insensitive to light and moisture and shouldl be a goodsolvent when melted for the dye used. In any of the forms shown one side of the filter paper, if it is to be'exposed on the surface o1' the fo'od package, may be printed or Aotherwise colored black to seal the contents of the pocket from deteriorating light waves. The sealed transparent envelope as provided protects the indicator against moisture. s l

Various colorv dyes may be used particularly in l the forms involving a plurality of indicating areas .35 v

In each `case the melting temperature of the solaccording to the packaged' gencies.

Having thus described our invention wenclaim and desire to secure by United States Letters Patent is:`

1. An indicator for temperatures reached while` an object is not under observation, comprising a sheet of absorbent material bearing a dye. substance` and a sheet bearinga solvent which liquees at a temperature ceeded and means for maintaining the twofsheets in cooperative relationship whereby the dye substance and solvent come inA contact with each other. Y 2..A temperature indicator comprising a sheet having a dry dye printed on one vface and a sheet having printed thereon a solid solvent for saiddye liqueabl'eat the temperature to which the indicator is designed'to respond, and means to secure the two sheets togetherwith the printed faces in contact.

3. An indicator as set forth in claim 2in which transparent envelope. f

` thesheetmatferial -isr encased in .a moisture proof 4. 'An indicator as set forth inclaim 2 in which one sheet of material is light proofed onvone side K v for use. or whether it may be tested or` used in'emer.-y

.which should not be exand the twosheets are inclosed in a moisture re- '7. An indicator as set forth in claim 6. each sistant transparent envelope. dye and solvent imprint having a calibrated area 5. An indicator as set forth in. claim 2 having adjacent thereto whereby the duration of the excertain portions of the absorbent sheet treated cessive temperatures can be estimated from the to resist the solvent whereby a pattern or message 5 spread of the dye spots in the calibrated areas.

will be formed thereon by the dyeing of the un- 8. A temperature indicator as set forth in claim treated portions of the sheet when the solvent is 6 in which the areas of the sheet material adjamelted. c'ent each dye and solvent imprintv are set off by v,6. A temperature indicator comprising a sheet areas of the sheet impermeable to the solvent. of absorbent material having a series of imprints l0 9. A temperature indicator as set forth in claim of dry dyes of different colors and imprints of 6 in which the areas ofthe sheet material adjasolvents for said dyes adjacent thereto, the solcent each dye and solvent imprint are separated vents melting at successively higher temperatures by slots cut between the areas and extending part along the series whereby the successive appearway between the imprints.

ance of the spots of different colors indicate a 15 RAYMOND PAUL SCHREIBER.

rise in temperature as high as the melting point WILLlAM MCC. LEE. of the solvent for that color.

CERTIFICATE oF CORRECTION. Patent Ne. 2,579,ii59. July 5, 1915.

RAYMOND PAUL SGRREIBER, ET AL.

It is hereby certified that error appears in the printed specification of the above numbered patent requiring correction as follows: Page l, sec-- ond column, line 5h., for "Sudan blue KA" read --Sudan blue `GA-; and that the said Letters Patent should be read with this correctionltherein that theeame may conform to the record of the case in the Patent Office.

signed and sealed this zndrdey er october, A. D. 19ir5.

Leslie l'r'azerv (seal) First Assistant cemieeie'ner ef Patente.

and the twosheets are inclosed in a moisture re- '7. An indicator as set forth in claim 6. each sistant transparent envelope. dye and solvent imprint having a calibrated area 5. An indicator as set forth in. claim 2 having adjacent thereto whereby the duration of the excertain portions of the absorbent sheet treated cessive temperatures can be estimated from the to resist the solvent whereby a pattern or message 5 spread of the dye spots in the calibrated areas.

will be formed thereon by the dyeing of the un- 8. A temperature indicator as set forth in claim treated portions of the sheet when the solvent is 6 in which the areas of the sheet material adjamelted. c'ent each dye and solvent imprintv are set off by v,6. A temperature indicator comprising a sheet areas of the sheet impermeable to the solvent. of absorbent material having a series of imprints l0 9. A temperature indicator as set forth in claim of dry dyes of different colors and imprints of 6 in which the areas ofthe sheet material adjasolvents for said dyes adjacent thereto, the solcent each dye and solvent imprint are separated vents melting at successively higher temperatures by slots cut between the areas and extending part along the series whereby the successive appearway between the imprints.

ance of the spots of different colors indicate a 15 RAYMOND PAUL SCHREIBER.

rise in temperature as high as the melting point WILLlAM MCC. LEE. of the solvent for that color.

CERTIFICATE oF CORRECTION. Patent Ne. 2,579,ii59. July 5, 1915.

RAYMOND PAUL SGRREIBER, ET AL.

It is hereby certified that error appears in the printed specification of the above numbered patent requiring correction as follows: Page l, sec-- ond column, line 5h., for "Sudan blue KA" read --Sudan blue `GA-; and that the said Letters Patent should be read with this correctionltherein that theeame may conform to the record of the case in the Patent Office.

signed and sealed this zndrdey er october, A. D. 19ir5.

Leslie l'r'azerv (seal) First Assistant cemieeie'ner ef Patente. 

